1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method, and particularly to an ink jet printing apparatus and an ink jet printing method for performing printing using a processing liquid that makes inks insoluble.
2. Description of the Prior Art
Ink jet printing apparatuses, which have advantages such as their capability of simple printing on various printing mediums, are enjoying more and more applications due to their improved print quality. Ink jet printers are not only used personally but also in offices in order to output various types of information, for example. The ink jet printing apparatuses are what are also used as printout apparatuses in facsimile machines, copy machines, and word processors or the like.
Thus, the ink jet printing apparatuses are further desired to provide a higher image quality. Specifically, it is desirable that printed characters such as black letters have high density and have sharp edges without feathering, that is, bleeding in a form of whiskers. In addition, in printing color images, bleeding is desirably prevented at boundaries between colors.
Some conventional methods, which increase the density (for example, OD: optical density) of black characters and form an image with sharp edges, use ink as a black (Bk) ink, what is called a remaining upper part-type ink, which permeates through a plain paper at a relatively low speed so that a coloring material remain at a upper part (shallower part) of a printing medium.
A problem with the use of such an remaining upper part-type ink of Bk, however, is that due to its insufficient fixing capability (permeability), a relatively long time is required to eject printed paper and obtain a printed product, especially to fix the printed image when solid images which have a particularly high duty are printed.
On the other hand, highly permeable inks have generally been used in order to prevent ink from bleeding at boundaries between colors in color images. In this case, however, when the Bk ink is also highly permeable, it is disadvantageously impossible to increase the density of black characters as described above or other problems may result in. In order to solve this problem, a remaining upper part-type Bk ink of lower permeability is used, while the other color inks are highly permeable. Additionally, the bleeding at the boundaries is prevented by allowing the Bk and color inks to be ejected in accordance with a fixed or more amount of time difference, or for the boundaries, by using a process black obtained through compounding from color inks. In this case, however, when printing black characters or the like, it may be caused that a fixing speed of the ink to the printing medium becomes lower and then printing with high speed can not be performed. The fast printing is desired particularly in the case that the ink jet printing apparatus used in offices.
In addition, a known means for improving, in particular, the fixing capability provides heaters along a paper feed path to evaporate moisture from the inks in order to promote fixation. This configuration enables faster fixing which contributes to faster printing.
As is apparent from the above description, it is relatively difficult for the conventional techniques to print high-grade black characters or the like and perform printing without bleeding at the boundaries between colors, with a relatively high speed. More specifically, a mere change in Bk ink permeability does not allow these problems to be simultaneously solved, particularly because there is a tradeoff relationship between the printed character grade such as the density and the fixing capability. This, in turn, can not provide a sufficient solution to the problem of bleeding at the boundaries.
The method of allowing the inks to be ejected at different points of time or using the process black as described above has difficulties in realizing fast printing. In addition, the method of using the heaters for fixing is not practical because more thermal energy is required to achieve fast printing.
The assignee of the present application has proposed use of a processing liquid for making color materials in ink insoluble, in order to improve the above-described black character grade or to improve color-developing capability. For example, the processing liquid is ejected before ejection of the ink so that the processing liquid reacts with the ink ejected after and much color material in the ink remains on a surface of the paper, thereby increasing the density and the color-developing capability and preventing feathering from occurring. In this case, the processing liquid with a relatively low permeation speed is conventionally used to create a pool of the processing liquid on the paper so that the ink can be applied to this pool. The ink thereby reacts on a surface of the paper as described above.
Disadvantageously, however, the use of the processing liquid with a low permeation speed is unsuitable for fast printing.
The object of the present invention is to provide an ink jet printing apparatus and an ink jet printing method that can realize fast printing based on fast fixing and that can print black characters with high density and little feathering and images with little bleeding at boundaries between colors.
Another object of the present invention is to provide an ink jet printing apparatus and an ink jet printing method that can achieve the above object and that can solve a problem that may occur when a head of a large printable width is used.
The problem caused by the use of the head of large width is an increase in temperature associated with continuous printing. When high-duty printing is continuously carried out, for example, the width of the head becomes longer to shift a landing position of the ink from a normal one. In the case that a plurality of heads are used for the inks and the processing liquid as described above, the landing position may vary among the heads, that is, a misregistration problem may occur.
Thus, it is another object of the present invention to avoid the misregistration between the inks and the processing liquid in order to achieve the above-described objects such as high-quality printing.
In a first aspect of the present invention, there is provided an ink jet printing method of performing printing by applying to a printing medium, an ink and a processing liquid for making a coloring material in the ink insoluble, the method comprising the steps of:
applying a black ink containing a black coloring material and the processing liquid to the printing medium to mix the black ink and the processing liquid together in a liquid state on the printing medium, and
applying, with a timing different from that for a reaction resulting from the mixture of the black ink and the processing liquid, a color ink to an area of the printing medium to which the black ink and the processing liquid are not applied.
In a second aspect of the present invention, there is provided an ink jet printing apparatus which uses a head for ejecting an ink and a head for ejecting a processing liquid for making a coloring material in the ink insoluble to perform printing by ejecting to a printing medium the ink and the processing liquid, the apparatus comprising:
ejection control means for ejecting a black ink containing a black coloring material and the processing liquid to the printing medium to mix the black ink and the processing liquid together in a liquid state on the printing medium, and
for ejecting, with a timing different from that for a reaction resulting from the mixture of the black ink and the processing liquid, a color ink to an area of the printing medium to which the black ink and the processing liquid are not ejected.
With this configuration, for example, the black ink is applied to the printing medium and the processing liquid is then applied so as to mix the black ink and the processing liquid together on the printing medium in a liquid state, and with a timing different from that for the reaction resulting from the mixture of the black ink and the processing liquid, for example, after the reaction, the color inks are applied to an area of the printing medium to which the black ink and the processing liquid are not applied. Thus, a reactant between the black ink and the processing liquid or the black ink becomes insoluble so as to be prevented from flowing out to the peripheries thereof, thereby reducing bleeding at the boundary between a color image and a black image even when the color ink is applied to the peripheries That is, when before the black ink becomes insoluble, the processing liquid or another ink is applied to the peripheries of the black ink, a liquid which has not become completely insoluble may flow out, but the present invention can prevent such a phenomenon.
In addition, when the processing liquid and the color inks are that permeate at a high speed, the black and color images can be printed with high fixing capability.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.